A fundamental issue in the analysis of the cellular basis of memory is the importance of the differential roles of regulatory cellular mechanisms in the transition between short- and long-term memory. One of the main differences between short- and long-term synaptic plasticity is the requirement for protein synthesis. The objective of the proposed research is to investigate the involvement of specific proteins that have been implicated in the cellular changes associated with long-term synaptic plasticity. Many proteins have been identified whose levels are altered as a result of long-term sensitization of defensive withdrawal reflexes of Aplysia, a well-studied model for long-term memory formation. One of these proteins has recently been identified as Aplysia tolloid/bone morphogenetic protein like-1 (apTBL-1). In other systems, homologues of apTBL-1 act as activators of the TGFbeta superfamily of growth factors. A previous study has shown that application of TGFbeta induces long-term facilitation of Aplysia sensory-motor connections in isolated ganglia. In Specific Aim 1, the ability of apTBL-1 to induce long-term synaptic facilitation, which partly mediates long-term sensitization, of cultured neurons will be tested. Further, the ability of a specific antibody against apTBL-1 will be tested for its ability to block the induction of long-term facilitation by 5-HT, a known neuromodulator. In Specific Aim 2, the ability of TGFbeta to produce long-term facilitation of cultured sensory-motor connections will be tested. This study will localize TGFbeta's action to either or both the sensory or motor neuron. The distribution of TGFbeta receptors will also be determined using immunohistochemical techniques. Western blots will be performed to confirm the specificity of the antibodies used for the staining. In Specific Aim 3, the signaling mechanisms which transduce TGFbeta signals to the nucleus will be investigated. Specifically, the activities of MAPK and the SMAD family of transcription factors will be analyzed for their roles in TGFbeta signaling. This project will provide insights into the molecular mechanisms underlying simple forms of learning.